This invention relates to methods and apparatus for isolating polymers for further processing from mixtures of polymers and water. As obtained from the polymerization vessel, polymerized compositions may contain up to about 90% by weight water, and it is often desirable to isolate the polymer from the water to produce a product containing less than about 5% by weight residual moisture.
Further, this invention relates to methods of isolation of a polymer from mixtures of the polymer and water wherein the specific gravity of the polymer is greater than that of water.
This invention is especially useful in the separation of fluoroelastomers from mixtures thereof in water.
Screw extrusion of materials such as elastomeric polymers is well known. During the extrusion process, minor amounts of residual moisture in the polymer may be removed through heating and working of the screw upon the polymeric material, by atmospheric or vacuum venting.
When the water content of such an elastomeric polymer is substantial, conventional screw extrusion is inadequate to effect water removal without serious impairment of process efficiency and/or product properties. Thus, when the water content is high, special methods must be employed to remove excessive amounts of water.
A method and apparatus for water removal from mixtures of plastic materials and water is disclosed in U.S. Pat. No. 3,035,306. That reference discloses a method and apparatus for removing water from plastic materials which are lighter than water to a degree of less than about 1% by weight residual moisture. The dewatering is accomplished by feeding a stream of synthetic rubber and water to a screw extrusion device such that the longitudinal axis of the screw is inclined upwards from the horizontal. Feeding of the synthetic/water mixture is through a feed port located at a vertical level below that of the extruder discharge port, and a drain opening for discharging water is provided, located below the feed port.
The separator described in U.S. Pat. No. 3,035,306 is also said to be useful for plastics which are heavier than water if the extruder separator is oriented such that its axis is directed downwardly with the feed end located vertically higher than the polymer discharge end. In practice, however, attempts to dewater fluoroelastomers by this process and using apparatus as described in the cited reference have proven unsatisfactory, since by this method excessive amounts of polymer were carried away by the discharging water.